From an employer's point of view, it's an embarrassment of riches, or option overload, if you will. Hiring managers are now taking up to twice as long to fill positions, not because they're having trouble finding viable candidates, but because there are so many good prospects out there, they're afraid that once they make their decision, an even better candidate will come along.
It's the same principle a lot of people use when looking for a spouse. "If I settle down with him/her today, what if someone even better turns up tomorrow?" With so many job candidates out there, you can hardly blame those doing the hiring.